Glass seal



H. M. ELsEY July 28, 1931.

GLASS SEAL Filed March 20, 1930 INVENTOR Howard M Else AT'TORNEY Mhl mmm UNITED sra'res PATENT: OFFICE mm I. may, or canon-r; rmsnvama, assrenon 'rownsr'menousu mm a; muracrume OOIIAI'YfA eonrona'rron or rmmvma erase an.

Application m larch a0, 1000. lerlal a. cam.

ilhis invention relates to glam seals and to methods of sealing molybdenum eading conductors into gas-tight tubes. An ob ect o; the invienbtion is to 1:118:80! 3 'htsealoramo enumconu r. gwhg has hitherto been used as an 1nleading conductor in vacuum tubes of certain kinds, notably those composed of boro-silicate glass. howegeri) a dd1lSad "van inbemg' relativ y rie,an-are wir a fthissubstancewillnot stand cod bending. M01 enum, on the other hand, will stand'col bendin and has properties which are at least as esirable as those of tungsten for hard-glass seals. Molybdenum however, one disadvantage that has hitherto limited itsuse in certain instances. This disadvan is that it oxidizes rather easily in a lasslowers flame and the ox de so rodu will prevent the attainment of a tig t seal if it gets between the molybdenum wire and the glass because it destroys the power of the one for the other. Furthermore, molybdenum oxide 1s apt to be a volatile at the workiugtemperature of the .glass and to cloud its surface. ob ect of the invention is to overcome thls difliculty so that the molybdenum elctrode can be tightly sealed in the tube,'and the tube assembled to have a clear transparent surface. Other objects of the invent1on w1ll become evident from the following detailed description, taken in eonjunctilolrh with the accomany1ng"draw1n sinw 35 P Figure 1 is avlew of the glam bead formed on a molybdenum wire as one of the nmaryste in forming the molybdenum-g ass a Fig. 2 is a partially side elevational and 9 partially sectional view illustrating the reerred method of sealing the beaded mo yb-- denum electrode in the press of a tube.

The molybdenum wire 10, to be used as an electrod as diselosedin F1 1,,has a glass beadll formedonitssankata int where the electrode will pass throng the of the tube. The upper art of the i may be ded outw y, as at 12.

The md 13 of wire, which is to extend inside ofthe glassapparatus, isthen cleaned,

oxide layer. This may be done either echanically-or by making it the cathode, at high current density in an alkaline bath. The surface of the molybdenum is. then preferably plated, as by electro-plating, very 'ghtly with copper which adheres very well to the molybdenum. Nickel is then preferably lated upon the copper to form with it, a ouble coating which revents the mol bdenum from oxidizin en the electro e is sealed into the tuie. If mercury is to be used in the tube, the cop r coating is not used. If desired, the mo y enum may be further protected by a plating of chromium on the nickel. I

The tube 14, into which the electrode is to be sealed, may be exhausted ofair by any suitable nonoxidizing or chemically inert gas, such as nitrogen, entering the tube through the opening 15, and the beaded electrode may then he slipped into the opening in the seal 16 of the lass tube, previously provided for the bead, and through which the nitrogen or other gas is escaping from the ap aratus.

e opening 16 for the beaded electrode should be of such size that the broad head 12 of the beadwill fit tightlywithin it. The stream of nitrogen or other may then be so cut oil, and the bead, witi its electrode, sealed in the glass. The densit of nitrogen is almost that of air, so that the twogases have about the same rate of efiusion. Accordingly, the nitrogen will not escape rapidly from the open end of the tube, and, In large tubes, the glass-blower can blow into the tube in working the seal without adding any oxidizin amount 'ofo gen to the nitron. The g as blower also be able to iiish the seal without the (glass being fogged by sublimed molybdic oxi e. In tubes that require very careful manufacture in regard to scaling and clear transparent a pearance, the use of thevarious steps out ined above is recommended. This is especially true where the tube is small, and the electrode and the inside of the glass cannot be reached for cleaning after the electrode is sealed. However, with a large pro- 3 any suitable means, until, it is free from portion of tubes, either the plating of the molybdenum electrode with a rotective coating before sealing or the working of the seal in an inert gas will be suflicient'to prevent the oxidation of the molybdenum. In other words, with certain tubes, the molybdenum may be Coated with a protected coating and then sealed by the glass-blower in the tube without further precaution against oxidizing the molybdenum. On the other hand, the mol bdenum electrode may be bare above its heat? and very carefully sealed into certain tubes in the presence of an inert nonoxidizin gas.

' Accor ingly, there has been disclosed a method of sealing an electrode of molybdenum in a gas-tight tube by which the electrode is very tightly sealed, and also in which the interior surface of the tube is not fogged by the molybdic oxide.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. The method of sealing a molybdenum electrode in a tube which comprises forming a bead on the shank of said electrode, cleaning the surface of said electrode, plating the surface of said electrode with a protective coating and sealing said beaded electrode into said tube.

2. The method of sealing a molybdenum electrode in a tube which comprises forming a bead on the shank of said electrode, inserting an inert gas into said tube and sealing said beaded electrode in said tube.

3. The method of sealing a molybdenum electrode in a tube which com rises forming a bead on the shank of said e ectrode plating the surface of said electrode, inserting an inert as into said tube and sealing said beadetf electrode in saidtube. I

In testimony whereof, I have hereunto subscribed my name this 15th day of March,

HOWARD M. ELSEY. 

